Glass sheets are used in the exterior and interior of buildings and in general industries, for instance, in windows, show windows, wall materials, doors, partitions, display cases, water tanks and furniture. At a corner of a window, show window or display case, two glass plates are joint at a desired angle with a frame made of metal, wood or plastic, and the joining parts between the glass plates and the frame are bound with a calking material such as silicone rubber and a sealing material. However, appearance and seeing through are disturbed by the frame at a corner. In addition, a stainless steel frame increases costs.
Alternatively, an edge of a glass sheet is matched with an edge of another glass sheet without using a frame and the matched edges are adhered with a calking material such as silicone rubber and a sealing material. However, appearance and seeing through at a corner is not so improved even in such a structure. Further, the adhered corner is weak in strength. In addition, calking materials and sealing materials have limited weatherability. Therefore, the life of the adhered part is relatively short in general.
In order to remove the aforesaid drawbacks, a method is known where a glass sheet is heated and bent to have a bend of a desired angle. For instance, a usual float method glass sheet is placed horizontally on a frame which has a desired angle, the whole glass sheet is heated at about 500.degree. to 580.degree. C. and a position of the glass sheet to be bent is further heated locally to about 700.degree. to 750.degree. C., and then the glass sheet is molded on the frame by gravity or other external force to have a bend of a desired angle. However, a radius of curvature of the bend is relatively large. When a glass sheet is 4 mm thick for instance, a radius of curvature is at least 35 to 40 mm. Accordingly, a window, water tank, show window or display case with such a bend will largely distort an object. Further, because a relatively broad area near the bend of a glass sheet is disposed to a temperature above an annealing point, warpage is seen after bending in such a relatively broad area. Thus, straight parts have large distortion. FIG. 10 is an illustrative cross-sectional view of a bend area of a glass sheet which is formed in the aforesaid method. A radius of curvature at a bend, B.sub.1, is approximately 10 times a thickness of the glass sheet, d. Parts, AB.sub.1 and AB.sub.2, are transitional areas with a length several times the thickness, d, between straight parts, A.sub.1 and A.sub.2 and a bend, B.sub.1, and are distorted with bad optical properties. In addition, straight parts, A.sub.1 and A.sub.2, cannot maintain their original flatness as before the heat processing due to exposure to a high temperature, and have seeing through distortion and reflection distortion.
U.S. Pat. No. 3,762,903 discloses a process for bending a glass sheet to a relatively sharp angle, which comprises applying a layer of electrically conducting material to at least one surface of the sheet along a line about which it is desired to bend the sheet, applying an electrical potential across said line of a sufficient magnitude and for a time adequate to heat the sheet in the area immediately adjacent said line to a temperature above the bending point of the glass, and bending said sheet along said line to form said relatively sharp angle therein. More specifically, a glass sheet is placed on a bending mold such as a V-shaped frame. The glass sheet and the mold are heated to a temperature of 900.degree. to 1,150.degree. C. F(i.e., 482.degree. to 621.degree. C.) in a furnace. Upon the glass sheet reaching the desired overall temperature, an electrical potential is applied to the line of the electrically conducting material to heat the glass sheet immediately adjacent the line to a temperature above the bending temperature of the glass, for instance, above 1,200.degree. F., i.e., 649.degree. C. Then the glass sheet is bent by gravity into conformity with the bending mold. Typically, a potential of 45 volts maximum is applied in a current of 3 amperes for 15 minutes.
Windshields and backlights for automobiles are intended there and, therefore, the illustrative thickness of a glass sheet is rather small, i.e., 0.090 inch or 2.3 mm.
U.S. Pat. No. 3,762,904 discloses a process which is similar to the aforesaid process of U.S. Pat. No. 3,762,903, but is different in that a groove is formed in a surface of a glass sheet along a line about which it is desired to bend the glass sheet and an electrically conducting path is formed on an ungrooved surface of the glass sheet opposite the groove.
It is known to fit plural glass sheets in a window in dual or more structure for protection against cold, particularly, in cold districts. Such a dual or more structure of glass sheets is often used also in show windows, display cases and the like as an exterior for the same purpose as stated above. A corner part of such windows, show windows and display cases is constructed in such a way that two or more glass sheets are faced to one another in a desired space with spacers being inserted, and the spacer areas are sealed with a calking agent such as silicone rubber and a sealing agent. Then, a set of glass sheets thus sealed is bound with another set of glass sheets at a desired angle with a frame made of metal, wood or plastic. In this prior art construction, the sealing agent such as butyl rubber for sealing the gap between glass sheet edges has insufficient weatherability. Therefore, a care is needed to protect the sealed part from direct irradiation with lights. To this end, the frame has a sufficiently large depth, which however obstructs appearance and seeing through at a corner. Further, a stainless steel frame increases costs. To solve the aforesaid shortcomings, it may be thought to match an edge of a glass sheet with an edge of another glass sheet with no frame and to adhere the matched edges to each other with a calking material such as silicone rubber and a sealing agent. However, the sealing agent such as butyl rubber is directly irradiated with lights and then its life is too short for practical use.